1. Technical Field
This invention relates to the non-intrusive testing of valves and, more particularly, to the testing of swing-type check valves using phased array sequence scanning.
2. Brief Description of the Prior Art
In the past, if someone wanted to see if a valve was operating properly flow through the valve was the first thing checked. If more information was desired, the valve could be taken apart. As technology advanced, other ways of checking the internal operation of the valve was developed. For example, a magnetic field may be used to determine the position of the disc in a check valve as is shown in U.S. Pat. No. 5,236,011. Also, ultrasonic vibrations have been used to monitor check valves to determine if they are operating properly. Even a combination of acoustic and magnetic techniques have been used in the past to monitor the operation of valves (see U.S. Pat. No. 5,008,841).
In the past, many different techniques of using ultrasonics have been developed to determine either the condition or the position of a valve without taking the valve apart. However, these non-intrusive inspection techniques normally did not give all of the information necessary to determine if a valve is operating properly. For example, the hinge pin on which the clapper of a check valve operates may be worn over a period of time. If this condition is not detected before the hinge pin breaks, a catastrophic failure would result. Typical non-intrusive inspection techniques are not able to detect wear on the hinge pin of a disc-type check valve.
In the last few years, the use of phased arrays to generate a wave front of ultrasonic signals has been used in different types of inspection techniques. For example, phased array has been used to measure flow of a fluid through a pipe as is shown in U.S. Pat. No. 7,503,227. Also variable angle ultrasonic transducers have been used in inspection techniques for pipes, conduit, plates or other foreign metallic members that may have irregularities in the surface of the test member (see U.S. Pat. No. 5,392,652).
As the capability of computers has increased dramatically in recent years, the use of a phased array ultrasonic signal has also been used in the testing of various equipment (see U.S. Patent Publication No. US 2009/0045994 A1). The use of phased array for three-dimensional ultrasonic inspection has also begun to be used in the industry (see U.S. Patent Publication No. US 2009/0293621 A1 and U.S. Pat. No. 7,784,347). Even combinations of laser beams and ultrasonic signals have been used in maintenance programs for testing equipment (see U.S. Pat. No. 7,728,967). Ultrasonic phased array has been used for some time in the testing of weld joints and pipes (U.S. Pat. No. 7,412,890).
As the nuclear regulatory industry has developed, a need has also developed for a very reliable method for non-intrusive inspection of the valves in a nuclear power plant. The operators needs to know with certainty that the valves are operating properly. Also, the operators need to know if a valve has begun to wear to the point where the valve should be serviced or repaired. This cannot be done with the inspection techniques that have been developed and used in the past.